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Video: Panda mourns loss of her baby at National Zoo

Closed captioning of: Panda mourns loss of her baby at National Zoo

>>>to the death of the new panda cup at the
national zoo
in washington, d.c. it lived for only six days, and now zoo officials are trying to figure out why. nbc's an thompson is there. ann, good morning to you.

>> reporter: good morning, matt. behind me you can see the cup's father. that is him showing off eating his breakfast. the lab results will not be back until the end of next week with you the initial examination shed a couple of things. found fluid in the cub's abdomen and found indications of liver problems, all issues that turn joy to sorrow here. this 2-month-old panda born and thriving at the
san diego zoo
is what they hoped for at the
national zoo
when its panda was born last week.

>>these bears are so
critically endangered
that every panda cub is important.

>> reporter: but on sunday zookeepers heard the cub's mother cry in distress. the cub, four ounces, the size of a stick of butter, was dead. for years zookeepers have tried to help her conceive. the odds are low and the mortality rate in captivity is high, 18%.

>>they are an
endangered species
so having the captive population is very important for the wild population.

>> reporter: today, only 1,600 giant pandas live in the wild in central and
southern china
, but whether free or in captivity, mating is not easy for these charismatic creatures. they are by nature loners, living on their own, and the females are only able to get pregnant once a year, in a short fertility window, lasting just 24 to
72 hours
. many zoos use artificial insemination.

>>very intensive effort because it's such a short window that you have to get the female pregnant, and so it is a very intensive effort. we work long hours during that time, and we monitor hormones and behavior and all of that to try to accomplish a pregnancy. ? in just a week of life the female cub clearly touched many. a short lived symbol of hope for a
threatened species
. now
tian tian
as you can see is working on his breakfast, typical behavior, pretty oblivious. don't really have a role other than in the initial conception -- any role in child-rearing. as far as mei jong goes, under 24-hour observation. the keeper says she's begun to eat and interact with them, and she has been cradling a plastic toy ever since her cub died. matt.